1. Field of the Invention
The present invention relates to a semiconductor element module used in a reception unit and a transmission unit in an optical communication system.
2. Related Background Art
An optical communication system using an optical fiber technique has been attracting attention in recent years. Since light-emitting and light-receiving elements are generally very small and are inconvenient for use as they are, they are usually provided in a semiconductor element module. A sleeve is formed in this semiconductor element module to connect this module to a ferrule having an optical fiber inserted therein.
A light-emitting diode is generally used as a light-emitting element. Since emitted light diffuses, the light is generally converged by a lens and guided into the optical fiber. Since light emitting from the end face of the optical fiber also diffuses, a lens must be provided between the optical fiber and the light-receiving element, thereby improving the ratio of light guided to the light-receiving element.
Hence, a lens must be provided between a semiconductor element, e.g., a light-emitting or light-receiving element, and the optical fiber. An example of a conventional module has a structure in which a lens is directly provided with a semiconductor element (e.g., Japanese Patent Laid-Open No. 4-165312 and the like). Another example has a structure in which a lens is provided in a module. When a lens is provided in a module, a metal holder 101 holding a lens 120 therein, as shown in FIG. 1, is mounted to a sleeve (not shown) which is formed separately from the metal holder 101. To hold a lens in a metal holder, a lens is held on a metal cylinder or the like.
At this time, SUS430, which is a material having a thermal expansion coefficient close to that of a glass material constituting the lens, is used as the material of the cylinder holding the lens. SUS303-based material having a good machining performance is used as the material constituting the sleeve.
Alternatively, as shown in FIG. 2, a light-emitting element is hermetically sealed by using a cap 201 that fixes a lens 220, and the cap 201 is mounted to a sleeve.